The present invention relates to a method for making simulated tofu products.
"Tofu" or possibly a soybean curd in contrast to a soy protein (acid precipitated) curd is one of the most popular, traditional soybean foods in Eastern Asia and is an important source of vegetable protein for people living in this region. It is edible in the form either cooked or not cooked and with or without a seasoning added and is a watery, white, jelly-like fragile food item having a moisture content as high as 88% by weight. In most cases, tofu is prepared by complicated manual processes. In a traditional process long-lasting in Japan, soybeans as a raw material are soaked in water for a prolonged period of time, for example, 8 to 24 hours according to the season, and the soaked soybeans are ground to form a slurry thereof. This slurry is then heated to extract the soy protein in the form as dissolved in liquid phase and subsequently filtered through a coarse cloth to remove insoluble soybean refuse which consists mainly of pulverized cellular substances and is generally known as "Okara" still utilizable for human and animal consumption. The filtrate, that is, soy milk, separated from the okara is subsequently coagulated to form a soy milk curd by the addition of a coagulating agent such as nontoxic alkaline earth metal salt, for example, calcium sulfate, calcium chloride or magnesium chloride. The soy milk curd so prepared is, before being submitted for human consumption, drained to remove the whey by placing it in a box traditionally made of wood and having a weighting lid, thereby completing the tofu.
In recently developed processes, certain organic gamma or delta lactones of aldonic and uronic acids, such as D-glucono-.delta.-lactone, are used as the coagulating agent and the necessity of the whey draining process has been eliminated. Notwithstanding this improvement, the prior art processes used for making the tofu still require many laborious, time-consuming procedures and generally are not suited for automated mass production line.
Apart from the genuine tofu made by the traditional methods including the recently improved ones, a simulated tofu is also well known and is currently available in the market in the form of a ready-to-cook or instant tofu. This simulated tofu is made by boiling an acqueous solution of powdery soybean protein isolate, adding a coagulating agent while the solution is boiled, and allowing the solution to cool.
A simulated tofu made without the addition of any coagulating agent is also known. For example, the Japanese Patent Publication No. 53-25015, published on July 24, 1978, the invention of which has been assigned to the same assignee of the present invention, discloses the simulated tofu made by uniformly mixing soybean protein isolate with 5 to 8 parts by weight of water and 0 to 4, preferably 0.5 to 2, parts by weight of edible oil, both relative to the total weight of the solids of the soybean protein isolate, and then heating the mixture to allow the latter to be coagulated by heat. The soybean protein isolate used therein is the one manufactured and sold under the trade name "Fujipro-R" by the assignee of the present invention and is specified as of a type having a gelling property so sufficient that a round cake of the soybean protein isolate, 3 mm in thickness and 3.5 cm in diameter, prepared by kneading a mixture of soybean protein isolate with 3.5 parts by weight of water relative to the total weight of the solids of the soybean protein isolate, heating the kneaded mixture in a boiled water for 30 minutes after having been filled in a casing of 3.5 cm in internal diameter, and cutting it to the predetermined dimensions after having been cooled, will neither crack nor break upon bending. In this known method, no coagulating agent is employed, it however involving the following disadvantages.
Physical properties of the simulated tofu product according to the above described known method, specifically, the hardness and the cohesiveness thereof as measured by the use of a testurometer, are similar to those exhibited by the genuine tofu. However, experiences have shown that the simulated tofu so prepared tends to give a sticky touch or sensation when a kitchen knife is passed in to cut it and also when the knife so passed in is being removed, and also to give a heavy sensation to the mouthfeel, those sensations being similar to that given by a "sesame tofu". The "sesame tofu", though it is a sort of simulated tofu, and is one of the traditional food items of Japan, is not a kind of proteinaceous gel made of bean curd but a kind of starchy gel made by heat-coagulating an acqueous mixture of an arrowroot starch with finely devided particles of sesame.
In view of the availability of the sesame tofu, those sensations afforded by the simulated tofu according to the above-mentioned publication are not of a nature unagreeable to consumers. However, we have long conducted a series of experiments to develop a method for making a simulated, ready-to-cook tofu product similar in physical property to that of the genuine tofu, the result of which has now matured to the present invention.